The first patient is a 74-year-old man, who became ill on 28 March 2013, and is now in critical condition. The other is a 66-year-old man who became ill on 29 March 2013 and is considered a mild case.

To date 18 cases (including these two new patients in Shanghai) of A(H7N9) have been confirmed in southern China, "including six deaths, ten severe cases and two mild cases," and over 500 more cases of people who have had close contact with the victims are being closely monitored.

Alarming as this illness may seem, the encouraging news (for now) is that there has been no evidence of human-to-human transmission – the patients who have been stricken ill all worked directly with poultry – but the key question is if it’s only a matter of time before the strain mutates into a virus that can spread between people.

According to the Huffington Post, what’s got scientists particularly worried about the A(H7N9) virus, which causes pneumonia-like symptoms and difficulty breathing, is that it appears to grow more easily in the body temperature environment of mammals’ bodies than the H1N5 strain from a few years back.

For now authorities have reassured the public that out of 34 randomly selected Huangpu River pig carcasses that have been tested so far, only one has tested positive for the A(H7N9) – but it remains to be seen if this sampling size is adequate enough to rule out a link.

And then there’s the matter of all the dead ducks, geese and swans found in the Nanhe River in Sichuan – Pulitzer prize winning science journalist Laurie Garrett, writing in Foreign Policy, reckons there is indeed a link between the dead birds and A(H7N9):

‘One very plausible explanation for this chain of Chinese events is that the H7N9 virus has undergone a mutation — perhaps among spring migrating birds around Lake Qinghai.

‘The mutation rendered the virus lethal for domestic ducks and swans.

‘Because many Chinese farmers raise both pigs and ducks, the animals can share water supplies and be in fighting proximity over food — the spread of flu from ducks to pigs, transforming avian flu into swine flu, has occurred many times.

‘Once influenza adapts to pig cells, it is often possible for the virus to take human-transmissible form.

‘That’s precisely what happened in 2009 with the H1N1 swine flu, which spread around the world in a massive, but thankfully not terribly virulent, pandemic.’

It all sounds pretty ominous, but is it time to freak out? Probably not – at this point you probably have a better chance of getting struck by lightning than coming down with A(H7N9), or even more likely one of the hundreds of other bugs that have been spreading through the city (and our office) now that the spring flu season is in full swing.

But if you think it better to be safe than sorry, the US Embassy has issued this advisory on a few precautions you can take (i.e. avoid eating runny eggs for breakfast) and over at myheathbeijing Dr Richard has a detailed post with additional tips.